Chlorzoxazone is a centrally acting muscle relaxant used to treat muscle spasm and the resulting pain or discomfort. It acts on the spinal cord by depressing reflexes. Our purpose is to investigate the effect of chlorzoxazone on moderate to severe postoperative pain after spine surgery. Our hypothesis is that chlorzoxazone can reduce postoperative pain and reduce opioidconsumption and side effects compared to placebo.